To protect fish and wildlife that depend on the water flow, the Southwest Florida Water Management District has proposed a minimum flow rate for the river. If it dips below that level, businesses would have to stop drawing water.

For the Mosaic Co., a phosphate company, that would mean shutting down its processing plant in Riverview when it can't pull water from Lithia and Buckhorn springs, which flow into the Alafia, officials told the water district. The company is currently permitted to draw about 6-million gallons a day from the springs.

The minimum-flow proposal was reviewed by an independent group of scientists. But before it can become official, the district must work with the businesses that would be affected by the change. The Alafia suffers from low water flow for nearly one-fifth of the year, scientists say.

The minimum flow would help protect fish and wildlife in the river, as well as the bay, where they end up, said Sid Flannery, a senior environmental scientist with the district.

"We determine how much water can come out for water supply without damaging the environment," Flannery said. "Only that quantity that can be removed without causing significant harm is available."

The lower Alafia River should be flowing at 120 cubic feet per second, scientists say. But before the minimum can be approved and enforced by water managers, major water users must create a plan.

Mosaic and Tampa Bay Water both pull millions of gallons from the lower Alafia River. Tampa Bay Water's permit will go through minor revisions because it's similar to the proposed standards.

Mosaic Fertilizer's permit is further off; partly its permit to draw water from Lithia and Buckhorn springs was established decades ago, before minimum flows were a big concern.

Mosaic officials told the water district they would be forced to shut down some of their operations if they can't draw water when the river is flowing below the minimum level. That happens about 18 percent of the year, Flannery said.

To comply with the upcoming standards, Mosaic is proposing to pull water from two wells near the southern part of the Alafia River. That water would be poured into the river and flow past the point where Mosaic draws water from Lithia and Buckhorn springs.

"It would definitely add to the flow level of the river, which would help the aquatic life there," Mosaic spokeswoman Christine Smith said.

The wells are already built and sit on the company's Fort Lonesome property in southeastern Hillsborough County. It hasn't used them in years. Mosaic is asking for a permit of about 6-million gallons a day, which is the same amount it's allowed to take from the Alafia River.

Some opponents to this idea say Mosaic shouldn't be pulling out any more precious groundwater.

But Robin Felix, spokeswoman for the Water Management District, said Mosaic is seeking to reduce the amount of groundwater it's permitted to use as part of its effort to consolidate water-use permits across five counties in Central Florida.

It would reduce its permits from about 100-million gallons a day to about 77-million gallons. Felix said the district is trying to help it find ways to reduce that even further.

Jessica Vander Velde can be reached at jvandervelde@sptimes.com or (813) 661-2443.